1. Field of the Invention
This invention relates to a three-dimensional sound reproducing apparatus which conducts sound reproduction with adding sound field effects corresponding to various three-dimensional acoustic spaces such as a concert hall, to an audio signal, and also to a three-dimensional sound reproduction method which can provide a listener with a three-dimensional sound with enhanced presence.
2. Background
In a three-dimensional acoustic space such as a concert hall, a sound generated by the player and the like is reflected from various portions such as walls of the hall and then reaches the listener's ear in the form of reverberation sounds from various directions. Such reverberation sounds from various directions function as a source of producing presence specific to the three-dimensional acoustic space. As an acoustic system which is intended to reproduce presence of a play in such a three-dimensional acoustic space with high fidelity, known is a so-called multispeaker system. In a multispeaker system, a number of loudspeakers which are arranged so as to surround a listener generate a sound and the volume of the sound is controlled, whereby a sound having an arbitrary sound location can be reproduced. Consequently, an impression that reverberation sounds seem to arrive from various directions, i.e., presence which is similar to that obtained in a three-dimensional acoustic space such as a concert hall can be given to the listener.
As described above, a so-called multispeaker system can provide a listener with a three-dimensional sound with rich presence. FIG. 17 shows an example of the configuration of such a multispeaker system. In the figure, SC designates a center localization loudspeaker which is driven by a center-channel audio signal C, SL designates a left localization loudspeaker which is driven by a left-channel audio signal L, SR designates a right localization loudspeaker which is driven by a right-channel audio signal R, and SN1 to SN7 designate nonlocalization loudspeakers which are driven by a nonlocalization audio signal N. As illustrated, these loudspeakers are arranged so as to surround a listener M. The loudspeakers SC, SL, and SR output sounds which respectively have predetermined sound image locations. The loudspeakers SN1 to SN7 output nonlocalized sounds such as a voice of a person which is heard from nowhere. These sounds are heard by the listener M.
In place of the configuration in which all the loudspeakers shown in FIG. 17 are used, another configuration may be employed such as that in which the center localization loudspeaker SC is omitted and the center-channel audio signal C is supplied to the left and right localization loudspeakers SL and SR, or that in which, among the nonlocalization loudspeakers, only two loudspeakers SN3 and SN5 are used or only one loudspeaker SN4 is used.
The audio signals may be supplied to the loudspeakers in various manners. When the center-channel audio signal C, the left-channel audio signal L, the right-channel audio signal R, and the nonlocalization audio signal N are to be independently supplied, the audio signals are supplied to the corresponding loudspeakers via power amplifiers 301 to 304 as shown in FIG. 18.
In the case where a recording system for recording an audio signal, and a reproducing system for reproducing the audio signal are separated from each other, it is required to reduce the amount of information of the audio signal which is to be transmitted from the recording system to the reproducing system. Therefore, an encoder 1002 such as that shown in FIG. 19 is used in the recording system. Specifically, an amplifier 401 provides the center-channel audio signal C with attenuation of −3 dB. The output signal of the amplifier 401 is added by adders 402 and 403 to the left- and right-channel audio signals L and R. On the other hand, an amplifier 404 provides the nonlocalization audio signal N with attenuation of −3 dB. Phase shifters 405 and 406 respectively output a signal which leads in phase by 90 deg. the output signal of the amplifier 404, and that which lags in phase by 90 deg. the output signal. The output signals of the adder 402 and the phase shifter 405 are added to each other by an adder 407, and then output as a left-channel audio signal L′. The output signals of the adder 403 and the phase shifter 406 are added to each other by an adder 408, and then output as a right-channel audio signal R′. In this way, audio signals of four channels are compressed into those of two channels, and then recorded onto a medium or transmitted via communication means.
When the two-channel audio signals obtained from the encoder are to be reproduced in a reproduction system, a decoder shown in FIG. 20 is used. The original four-channel audio signals L, R, C, and N are reconstructed from the two-channel audio signals L′ and R′ and then supplied to the corresponding loudspeakers. In FIG. 20, 411 and 412 designate adders, 413 designates a phase inverter, and 414 to 417 designate power amplifiers.
The multispeaker system described above is excellent from the viewpoints of the sound field effect and provision of a three-dimensional sound with enhanced presence. However, the system must be realized by a large-scaled configuration using a number of loudspeakers, and hence the system itself is very expensive. When the multispeaker system is to be used, the loudspeakers must be placed at respective predetermined positions, and hence a sound room of a substantially large area is required. In the multispeaker system, the sound image location is controlled by balancing the volumes of the outputs of the loudspeakers. When the volumes fail to be balanced, therefore, an impression that the sound is generated by a loudspeaker inevitably prevails. Consequently, there arises a problem in that it is difficult to control sound reproduction with enhanced presence.
On the other hand, in another example of a conventional electronic instrument shown in FIG. 9, left and right loudspeakers 201L′ and 201R′ are respectively placed at the end portions of the instrument, and a sound carrying a spacial impression is generated by adjusting the balance of the volumes of the sound outputs of the loudspeakers. In order to generate a sound carrying a spacial impression by such a volume adjustment, the loudspeakers 201L′ and 201R′ must be placed at positions which are separated from each other by a fixed distance or longer. Therefore, the conventional electronic instrument has a problem in that its width is inevitably increased.